(1) Field of the Invention
The present invention relates to heat-sensitive transfer materials, and more specifically to heat-sensitive recording materials useful in a thermal ink-transfer recording process or a sublimation ink-transfer recording process.
(2) Description of the Related Art
Conventionally-known transfer recording processes include thermal ink-transfer recording processes and sublimation ink-transfer recording processes. According to the former processes, a heat-resistant recording layer is formed on a base sheet such as a polyester film by having a dye or pigment carried together with a binder resin on one side of base sheet. The base sheet is heated in a pattern from the back side thereof so that the dye or pigment is transferred onto another material. According to the latter processes, a dye alone is caused to sublimate so that it is transferred onto another material.
In each of these processes, thermal energy is applied from the back side of a base sheet in each of these processes. The back side of a heat-sensitive transfer material to be employed is, therefore, required to have sufficient lubricity, releasability, non-stickiness and the like so that a thermal head does not stick on the back side, in other words, does not develop any sticking problem.
It has therefore been the conventional practice to form a layer of a silicone resin, melamine resin, phenol resin, polyimide resin, epoxy resin or modified cellulose resin or a mixture thereof on the back side of a base sheet in a heat-sensitive recording material (see Japanese Patent Publication No. 58-13359).
Most of these resins are, however, thermosetting resins making use of various curing agents. A heating step is, therefore, required for curing upon formation of a heat-resistant layer on a heat-sensitive recording material, leading to the problem that the production process is cumbersome. Moreover, so-formed heat-resistant layer itself is weak and is inferior in adhesion in spite of its high melting point, leading to the problem that the film layer may peel off as dust particles upon printing and may give a trouble to a thermal head.
With a view toward overcoming the problems described above, it has been proposed to add an isocyanate or the like to a thermoplastic resin such as an acrylic resin, polyurethane resin, polyester resin or polybutadiene resin and then to cure the resulting resin to provide a heat-resistant layer and, further, to incorporate a lubricant or the like in the resulting resin to allow a printing device to smoothly slide thereon (Japanese Patent Application Laid-Open No. 225994/1984).
According to the above patent publication, the curing of the isocyanate is said to proceed at room temperature. In practice, however, the above proposal has the problems that the pot life is insufficient and the resulting resin may not be cured sufficiently due to reactions of the isocyanate with water and other impurities. In addition, the lubricant added to provide the heat-resistant layer with smooth sliding property is accompanied by the potential problems that it may bleed out if stored for a long time, or may produce dusts on a head during printing.
The present assignees have already proposed that the use of a silicone copolymer resin in stead of the above-mentioned resins for the formation of a heat-resistant layer can provide a heat-sensitive recording material excellent in various properties such as heat resistance, lubricity and non-stickiness (see Japanese Patent Application Laid-Open Nos. 61-227087 and 62-202786).